Ahead of Turkey's election, protesters threw stones at Istanbul Mayor Ekrem Imamoglu, a member of the main opposition Republican People's Party (CHP), during a campaign rally in the eastern city of Erzurum, a stronghold of Erdogan's party.
This was reported by the Reuters agency.
During a rally in Erzurum, Istanbul Mayor Imamoglu, who will become vice president if main opposition candidate Kemal Kilicdaroglu wins the election, addressed his supporters from the roof of an open-air bus.
At the same time, some people from the crowd started throwing stones at him and his supporters.
Imamoglu interrupted his speech and left the scene. "We are going for your safety," Imamoglu told his supporters.
He added that he would file a criminal complaint against the governor of Erzurum and the police chief for allowing the violence.
Video footage shows that at least one person was injured. Imamoglu later said that nine people were wounded.
In the 2018 presidential election, Erdogan won 72% of the vote in Erzurum, where most of his supporters live.
Presidential and parliamentary elections will be held in Turkey on May 14. Opinion polls show Erdogan faces the biggest electoral challenge of his two decades in power.
At a campaign rally on Sunday, Erdogan promised to "bury in the ballot boxes" the opposition for supporting LGBT people.
